pwm: rockchip: Convert to use dev_err_probe()

It's fine to call dev_err_probe() in ->probe() when error code is known.
Convert the driver to use dev_err_probe().

Signed-off-by: zhaoxiao <zhaoxiao@uniontech.com>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>